This invention relates to a profile stitcher which stitches together workpiece fabrics clamped between two profiled frames whose profile is similar to the stitch path and whose outer edges are fed by a contacting roller such that stitching through the profiled frame as a template is conducted and, more particularly, to controlling the speed of the conducting roller such that the stitch pitch through curved portions of the stitch path are kept the same as through straight portions of the stitch path.
Profile stitching is used to combine pieces of fabric when the pattern of stitch combination is applicable in mass usage. A profile stitcher is a template whereby the stitch path follows the shape laid out by the profile.
Referring FIGS. 5 through 7, one type of automatic profile stitcher is hereafter explained. The stitching path consists of both straight lines and curved lines. Two fabrics are clamped between an upper frame 1 and a lower frame 2. A groove 3 whose shape is similar to the profile of the frames 1, 2 is provided through both the upper and lower frames. A projection 4a projected from a throat plate 4 inserts loosely into the groove 3, and a roller 5 which is frictionaly contacted to the outer profiled edge of the frames is rotated at constant speed in association with the up-down motion of a needle. The roller rotates such that the frames 1, 2 are guided by the projection 4a. The needle flows through a needle entry n provided in the projection 4a allowing stitching along the groove 3.
FIG. 6 shows a stitch line stitched through the profiled frame shown in FIG. 5. Since the speed of the roller 5 is constant, stitch pitch at the curved portion I.sub.2 is narrower than stitch pitch at the straight portion I.sub.1. Thus, the stitching quality is poor. When the straight portion I.sub.1 is stitched, its feed length is same as the circumference length of the roller 5. This, however, is not the case when the stitch path is a curve. Referring to FIG. 7, when the curved portion I.sub.2 is stitched, radius R.sub.2 of the curved stitch line is shorter than radius R.sub.1 of the outer curved portion 1a, 2a of the profiled frame.
Thereby, because the outer curved portion 1a, 2a is conducted by the roller 5 and the stitch pitch length 1.sub.1 is expressed as 1.sub.1 =(2.pi.r.sub.1 /360).times..theta..sub.1 ; where r.sub.1 denotes a radius of the roller 5 and .theta..sub.1 denotes the rotated angles of the roller 5 per one stitch; the stitch pitch length at the curved portion in the groove 3 is actually smaller than 1.sub.1 .
Accordingly, the stitch pitch at the curved portion I.sub.2 in FIG. 6 becomes smaller, and the stitching quality is degraded due to the imbalanced stitch-pitch.
Therefore, it is an object of the present invention to improve the stitching quality conducted by the profile stitcher.
It is a further object of the present invention to conduct profile stitching with equal stitch pitch through both curved portions and straight portions of the stitch line.